Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting a scheduling assignment signal for Device-to-Device (D2D) communication in a wireless communication system.
Discussion of the Related Art
As an example of a wireless communication system to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE; hereinafter, “LTE”) communication system is broadly described below.
FIG. 1 is a diagram schematically illustrating an E-UMTS network structure as an example of a wireless communication system. The Evolved Universal Mobile Telecommunications System (E-UMTS) is a system evolved from the conventional UMTS. A basic standardization process for the E-UMTS is being carried out in the current 3GPP. Generally, the E-UMTS may be referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and the E-UMTS, reference may be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), base stations (eNode B, eNB), and an Access Gateway (AG), which is located at an end of a network (E-UTRAN) and connected to an external network. The base stations may simultaneously transmit multiple data streams for a broadcast service, a multicast service and/or a unicast service.
One or more cells may exist for one eNB. One cell is set to one of bandwidths of 1.44, 3, 5, 10, 15, and 20 Mhz to provide a downlink or uplink transport service to several UEs. Different cells may be configured to provide different bandwidths. An eNB controls transmission/reception data to/from multiple UEs. For downlink (DL) data, the eNB transmits DL scheduling information to a UE to notify information related to time/frequency regions in which data will be transmitted, encoding, data size, and hybrid automatic repeat, and request (HARQ)-related information to the UE. For uplink (UL) data, the eNB transmits UL scheduling information to the corresponding UE to notify the UE of the time/frequency regions that can be used by the UE, encoding, data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A core network (CN) may include an access gateway (AG) and a network node for user registration of the UE. The AG manages mobility of a UE on the tracking area (TA)-by-TA basis, wherein one TA includes a plurality of cells.
The wireless communication technology has been developed up to the LTE based upon WCDMA. However, the demands and expectations from the users and the communication operators are consistently growing. In addition, since other wireless access technologies are constantly being developed, the wireless communication technology is required to evolve in order to secure competitiveness in the future. Accordingly, cost reduction per bit, enhanced service availability, use of a flexible frequency band, a simple structure and open interface, and proper power consumption of the UE are requested.